/* ----------------------------------------------------------------------
* Copyright (C) 2010-2014 ARM Limited. All rights reserved.
*
* $Date:        19. March 2015
* $Revision: 	V.1.4.5
*
* Project: 	    CMSIS DSP Library
* Title:	    arm_cfft_radix4_q15.c
*
* Description:	This file has function definition of Radix-4 FFT & IFFT function and
*				In-place bit reversal using bit reversal table
*
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*   - Redistributions of source code must retain the above copyright
*     notice, this list of conditions and the following disclaimer.
*   - Redistributions in binary form must reproduce the above copyright
*     notice, this list of conditions and the following disclaimer in
*     the documentation and/or other materials provided with the
*     distribution.
*   - Neither the name of ARM LIMITED nor the names of its contributors
*     may be used to endorse or promote products derived from this
*     software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
* -------------------------------------------------------------------- */

#include "arm_math.h"


void arm_radix4_butterfly_q15(
    q15_t *pSrc16,
    uint32_t fftLen,
    q15_t *pCoef16,
    uint32_t twidCoefModifier);

void arm_radix4_butterfly_inverse_q15(
    q15_t *pSrc16,
    uint32_t fftLen,
    q15_t *pCoef16,
    uint32_t twidCoefModifier);

void arm_bitreversal_q15(
    q15_t *pSrc,
    uint32_t fftLen,
    uint16_t bitRevFactor,
    uint16_t *pBitRevTab);

/**
 * @ingroup groupTransforms
 */

/**
 * @addtogroup ComplexFFT
 * @{
 */


/**
 * @details
 * @brief Processing function for the Q15 CFFT/CIFFT.
 * @deprecated Do not use this function.  It has been superseded by \ref arm_cfft_q15 and will be removed
 * @param[in]      *S    points to an instance of the Q15 CFFT/CIFFT structure.
 * @param[in, out] *pSrc points to the complex data buffer. Processing occurs in-place.
 * @return none.
 *
 * \par Input and output formats:
 * \par
 * Internally input is downscaled by 2 for every stage to avoid saturations inside CFFT/CIFFT process.
 * Hence the output format is different for different FFT sizes.
 * The input and output formats for different FFT sizes and number of bits to upscale are mentioned in the tables below for CFFT and CIFFT:
 * \par
 * \image html CFFTQ15.gif "Input and Output Formats for Q15 CFFT"
 * \image html CIFFTQ15.gif "Input and Output Formats for Q15 CIFFT"
 */

void arm_cfft_radix4_q15(
    const arm_cfft_radix4_instance_q15 *S,
    q15_t *pSrc)
{
    if(S->ifftFlag == 1u)
    {
        /*  Complex IFFT radix-4  */
        arm_radix4_butterfly_inverse_q15(pSrc, S->fftLen, S->pTwiddle,
                                         S->twidCoefModifier);
    }
    else
    {
        /*  Complex FFT radix-4  */
        arm_radix4_butterfly_q15(pSrc, S->fftLen, S->pTwiddle,
                                 S->twidCoefModifier);
    }

    if(S->bitReverseFlag == 1u)
    {
        /*  Bit Reversal */
        arm_bitreversal_q15(pSrc, S->fftLen, S->bitRevFactor, S->pBitRevTable);
    }

}

/**
 * @} end of ComplexFFT group
 */

/*
* Radix-4 FFT algorithm used is :
*
* Input real and imaginary data:
* x(n) = xa + j * ya
* x(n+N/4 ) = xb + j * yb
* x(n+N/2 ) = xc + j * yc
* x(n+3N 4) = xd + j * yd
*
*
* Output real and imaginary data:
* x(4r) = xa'+ j * ya'
* x(4r+1) = xb'+ j * yb'
* x(4r+2) = xc'+ j * yc'
* x(4r+3) = xd'+ j * yd'
*
*
* Twiddle factors for radix-4 FFT:
* Wn = co1 + j * (- si1)
* W2n = co2 + j * (- si2)
* W3n = co3 + j * (- si3)

* The real and imaginary output values for the radix-4 butterfly are
* xa' = xa + xb + xc + xd
* ya' = ya + yb + yc + yd
* xb' = (xa+yb-xc-yd)* co1 + (ya-xb-yc+xd)* (si1)
* yb' = (ya-xb-yc+xd)* co1 - (xa+yb-xc-yd)* (si1)
* xc' = (xa-xb+xc-xd)* co2 + (ya-yb+yc-yd)* (si2)
* yc' = (ya-yb+yc-yd)* co2 - (xa-xb+xc-xd)* (si2)
* xd' = (xa-yb-xc+yd)* co3 + (ya+xb-yc-xd)* (si3)
* yd' = (ya+xb-yc-xd)* co3 - (xa-yb-xc+yd)* (si3)
*
*/

/**
 * @brief  Core function for the Q15 CFFT butterfly process.
 * @param[in, out] *pSrc16          points to the in-place buffer of Q15 data type.
 * @param[in]      fftLen           length of the FFT.
 * @param[in]      *pCoef16         points to twiddle coefficient buffer.
 * @param[in]      twidCoefModifier twiddle coefficient modifier that supports different size FFTs with the same twiddle factor table.
 * @return none.
 */

void arm_radix4_butterfly_q15(
    q15_t *pSrc16,
    uint32_t fftLen,
    q15_t *pCoef16,
    uint32_t twidCoefModifier)
{

#ifndef ARM_MATH_CM0_FAMILY

    /* Run the below code for Cortex-M4 and Cortex-M3 */

    q31_t R, S, T, U;
    q31_t C1, C2, C3, out1, out2;
    uint32_t n1, n2, ic, i0, j, k;

    q15_t *ptr1;
    q15_t *pSi0;
    q15_t *pSi1;
    q15_t *pSi2;
    q15_t *pSi3;

    q31_t xaya, xbyb, xcyc, xdyd;

    /* Total process is divided into three stages */

    /* process first stage, middle stages, & last stage */

    /*  Initializations for the first stage */
    n2 = fftLen;
    n1 = n2;

    /* n2 = fftLen/4 */
    n2 >>= 2u;

    /* Index for twiddle coefficient */
    ic = 0u;

    /* Index for input read and output write */
    j = n2;

    pSi0 = pSrc16;
    pSi1 = pSi0 + 2 * n2;
    pSi2 = pSi1 + 2 * n2;
    pSi3 = pSi2 + 2 * n2;

    /* Input is in 1.15(q15) format */

    /*  start of first stage process */
    do
    {
        /*  Butterfly implementation */

        /*  Reading i0, i0+fftLen/2 inputs */
        /* Read ya (real), xa(imag) input */
        T = _SIMD32_OFFSET(pSi0);
        T = __SHADD16(T, 0); // this is just a SIMD arithmetic shift right by 1
        T = __SHADD16(T, 0); // it turns out doing this twice is 2 cycles, the alternative takes 3 cycles
        //in = ((int16_t) (T & 0xFFFF)) >> 2;       // alternative code that takes 3 cycles
        //T = ((T >> 2) & 0xFFFF0000) | (in & 0xFFFF);

        /* Read yc (real), xc(imag) input */
        S = _SIMD32_OFFSET(pSi2);
        S = __SHADD16(S, 0);
        S = __SHADD16(S, 0);

        /* R = packed((ya + yc), (xa + xc) ) */
        R = __QADD16(T, S);

        /* S = packed((ya - yc), (xa - xc) ) */
        S = __QSUB16(T, S);

        /*  Reading i0+fftLen/4 , i0+3fftLen/4 inputs */
        /* Read yb (real), xb(imag) input */
        T = _SIMD32_OFFSET(pSi1);
        T = __SHADD16(T, 0);
        T = __SHADD16(T, 0);

        /* Read yd (real), xd(imag) input */
        U = _SIMD32_OFFSET(pSi3);
        U = __SHADD16(U, 0);
        U = __SHADD16(U, 0);

        /* T = packed((yb + yd), (xb + xd) ) */
        T = __QADD16(T, U);

        /*  writing the butterfly processed i0 sample */
        /* xa' = xa + xb + xc + xd */
        /* ya' = ya + yb + yc + yd */
        _SIMD32_OFFSET(pSi0) = __SHADD16(R, T);
        pSi0 += 2;

        /* R = packed((ya + yc) - (yb + yd), (xa + xc)- (xb + xd)) */
        R = __QSUB16(R, T);

        /* co2 & si2 are read from SIMD Coefficient pointer */
        C2 = _SIMD32_OFFSET(pCoef16 + (4u * ic));

#ifndef ARM_MATH_BIG_ENDIAN

        /* xc' = (xa-xb+xc-xd)* co2 + (ya-yb+yc-yd)* (si2) */
        out1 = __SMUAD(C2, R) >> 16u;
        /* yc' = (ya-yb+yc-yd)* co2 - (xa-xb+xc-xd)* (si2) */
        out2 = __SMUSDX(C2, R);

#else

        /* xc' = (ya-yb+yc-yd)* co2 - (xa-xb+xc-xd)* (si2) */
        out1 = __SMUSDX(R, C2) >> 16u;
        /* yc' = (xa-xb+xc-xd)* co2 + (ya-yb+yc-yd)* (si2) */
        out2 = __SMUAD(C2, R);

#endif /*      #ifndef ARM_MATH_BIG_ENDIAN     */

        /*  Reading i0+fftLen/4 */
        /* T = packed(yb, xb) */
        T = _SIMD32_OFFSET(pSi1);
        T = __SHADD16(T, 0);
        T = __SHADD16(T, 0);

        /* writing the butterfly processed i0 + fftLen/4 sample */
        /* writing output(xc', yc') in little endian format */
        _SIMD32_OFFSET(pSi1) =
            (q31_t) ((out2) & 0xFFFF0000) | (out1 & 0x0000FFFF);
        pSi1 += 2;

        /*  Butterfly calculations */
        /* U = packed(yd, xd) */
        U = _SIMD32_OFFSET(pSi3);
        U = __SHADD16(U, 0);
        U = __SHADD16(U, 0);

        /* T = packed(yb-yd, xb-xd) */
        T = __QSUB16(T, U);

#ifndef ARM_MATH_BIG_ENDIAN

        /* R = packed((ya-yc) + (xb- xd) , (xa-xc) - (yb-yd)) */
        R = __QASX(S, T);
        /* S = packed((ya-yc) - (xb- xd),  (xa-xc) + (yb-yd)) */
        S = __QSAX(S, T);

#else

        /* R = packed((ya-yc) + (xb- xd) , (xa-xc) - (yb-yd)) */
        R = __QSAX(S, T);
        /* S = packed((ya-yc) - (xb- xd),  (xa-xc) + (yb-yd)) */
        S = __QASX(S, T);

#endif /*      #ifndef ARM_MATH_BIG_ENDIAN     */

        /* co1 & si1 are read from SIMD Coefficient pointer */
        C1 = _SIMD32_OFFSET(pCoef16 + (2u * ic));
        /*  Butterfly process for the i0+fftLen/2 sample */

#ifndef ARM_MATH_BIG_ENDIAN

        /* xb' = (xa+yb-xc-yd)* co1 + (ya-xb-yc+xd)* (si1) */
        out1 = __SMUAD(C1, S) >> 16u;
        /* yb' = (ya-xb-yc+xd)* co1 - (xa+yb-xc-yd)* (si1) */
        out2 = __SMUSDX(C1, S);

#else

        /* xb' = (ya-xb-yc+xd)* co1 - (xa+yb-xc-yd)* (si1) */
        out1 = __SMUSDX(S, C1) >> 16u;
        /* yb' = (xa+yb-xc-yd)* co1 + (ya-xb-yc+xd)* (si1) */
        out2 = __SMUAD(C1, S);

#endif /*      #ifndef ARM_MATH_BIG_ENDIAN     */

        /* writing output(xb', yb') in little endian format */
        _SIMD32_OFFSET(pSi2) =
            ((out2) & 0xFFFF0000) | ((out1) & 0x0000FFFF);
        pSi2 += 2;


        /* co3 & si3 are read from SIMD Coefficient pointer */
        C3 = _SIMD32_OFFSET(pCoef16 + (6u * ic));
        /*  Butterfly process for the i0+3fftLen/4 sample */

#ifndef ARM_MATH_BIG_ENDIAN

        /* xd' = (xa-yb-xc+yd)* co3 + (ya+xb-yc-xd)* (si3) */
        out1 = __SMUAD(C3, R) >> 16u;
        /* yd' = (ya+xb-yc-xd)* co3 - (xa-yb-xc+yd)* (si3) */
        out2 = __SMUSDX(C3, R);

#else

        /* xd' = (ya+xb-yc-xd)* co3 - (xa-yb-xc+yd)* (si3) */
        out1 = __SMUSDX(R, C3) >> 16u;
        /* yd' = (xa-yb-xc+yd)* co3 + (ya+xb-yc-xd)* (si3) */
        out2 = __SMUAD(C3, R);

#endif /*      #ifndef ARM_MATH_BIG_ENDIAN     */

        /* writing output(xd', yd') in little endian format */
        _SIMD32_OFFSET(pSi3) =
            ((out2) & 0xFFFF0000) | (out1 & 0x0000FFFF);
        pSi3 += 2;

        /*  Twiddle coefficients index modifier */
        ic = ic + twidCoefModifier;

    }
    while(--j);
    /* data is in 4.11(q11) format */

    /* end of first stage process */


    /* start of middle stage process */

    /*  Twiddle coefficients index modifier */
    twidCoefModifier <<= 2u;

    /*  Calculation of Middle stage */
    for (k = fftLen / 4u; k > 4u; k >>= 2u)
    {
        /*  Initializations for the middle stage */
        n1 = n2;
        n2 >>= 2u;
        ic = 0u;

        for (j = 0u; j <= (n2 - 1u); j++)
        {
            /*  index calculation for the coefficients */
            C1 = _SIMD32_OFFSET(pCoef16 + (2u * ic));
            C2 = _SIMD32_OFFSET(pCoef16 + (4u * ic));
            C3 = _SIMD32_OFFSET(pCoef16 + (6u * ic));

            /*  Twiddle coefficients index modifier */
            ic = ic + twidCoefModifier;

            pSi0 = pSrc16 + 2 * j;
            pSi1 = pSi0 + 2 * n2;
            pSi2 = pSi1 + 2 * n2;
            pSi3 = pSi2 + 2 * n2;

            /*  Butterfly implementation */
            for (i0 = j; i0 < fftLen; i0 += n1)
            {
                /*  Reading i0, i0+fftLen/2 inputs */
                /* Read ya (real), xa(imag) input */
                T = _SIMD32_OFFSET(pSi0);

                /* Read yc (real), xc(imag) input */
                S = _SIMD32_OFFSET(pSi2);

                /* R = packed( (ya + yc), (xa + xc)) */
                R = __QADD16(T, S);

                /* S = packed((ya - yc), (xa - xc)) */
                S = __QSUB16(T, S);

                /*  Reading i0+fftLen/4 , i0+3fftLen/4 inputs */
                /* Read yb (real), xb(imag) input */
                T = _SIMD32_OFFSET(pSi1);

                /* Read yd (real), xd(imag) input */
                U = _SIMD32_OFFSET(pSi3);

                /* T = packed( (yb + yd), (xb + xd)) */
                T = __QADD16(T, U);

                /*  writing the butterfly processed i0 sample */

                /* xa' = xa + xb + xc + xd */
                /* ya' = ya + yb + yc + yd */
                out1 = __SHADD16(R, T);
                out1 = __SHADD16(out1, 0);
                _SIMD32_OFFSET(pSi0) = out1;
                pSi0 += 2 * n1;

                /* R = packed( (ya + yc) - (yb + yd), (xa + xc) - (xb + xd)) */
                R = __SHSUB16(R, T);

#ifndef ARM_MATH_BIG_ENDIAN

                /* (ya-yb+yc-yd)* (si2) + (xa-xb+xc-xd)* co2 */
                out1 = __SMUAD(C2, R) >> 16u;

                /* (ya-yb+yc-yd)* co2 - (xa-xb+xc-xd)* (si2) */
                out2 = __SMUSDX(C2, R);

#else

                /* (ya-yb+yc-yd)* co2 - (xa-xb+xc-xd)* (si2) */
                out1 = __SMUSDX(R, C2) >> 16u;

                /* (ya-yb+yc-yd)* (si2) + (xa-xb+xc-xd)* co2 */
                out2 = __SMUAD(C2, R);

#endif /*      #ifndef ARM_MATH_BIG_ENDIAN     */

                /*  Reading i0+3fftLen/4 */
                /* Read yb (real), xb(imag) input */
                T = _SIMD32_OFFSET(pSi1);

                /*  writing the butterfly processed i0 + fftLen/4 sample */
                /* xc' = (xa-xb+xc-xd)* co2 + (ya-yb+yc-yd)* (si2) */
                /* yc' = (ya-yb+yc-yd)* co2 - (xa-xb+xc-xd)* (si2) */
                _SIMD32_OFFSET(pSi1) =
                    ((out2) & 0xFFFF0000) | (out1 & 0x0000FFFF);
                pSi1 += 2 * n1;

                /*  Butterfly calculations */

                /* Read yd (real), xd(imag) input */
                U = _SIMD32_OFFSET(pSi3);

                /* T = packed(yb-yd, xb-xd) */
                T = __QSUB16(T, U);

#ifndef ARM_MATH_BIG_ENDIAN

                /* R = packed((ya-yc) + (xb- xd) , (xa-xc) - (yb-yd)) */
                R = __SHASX(S, T);

                /* S = packed((ya-yc) - (xb- xd),  (xa-xc) + (yb-yd)) */
                S = __SHSAX(S, T);


                /*  Butterfly process for the i0+fftLen/2 sample */
                out1 = __SMUAD(C1, S) >> 16u;
                out2 = __SMUSDX(C1, S);

#else

                /* R = packed((ya-yc) + (xb- xd) , (xa-xc) - (yb-yd)) */
                R = __SHSAX(S, T);

                /* S = packed((ya-yc) - (xb- xd),  (xa-xc) + (yb-yd)) */
                S = __SHASX(S, T);


                /*  Butterfly process for the i0+fftLen/2 sample */
                out1 = __SMUSDX(S, C1) >> 16u;
                out2 = __SMUAD(C1, S);

#endif /*      #ifndef ARM_MATH_BIG_ENDIAN     */

                /* xb' = (xa+yb-xc-yd)* co1 + (ya-xb-yc+xd)* (si1) */
                /* yb' = (ya-xb-yc+xd)* co1 - (xa+yb-xc-yd)* (si1) */
                _SIMD32_OFFSET(pSi2) =
                    ((out2) & 0xFFFF0000) | (out1 & 0x0000FFFF);
                pSi2 += 2 * n1;

                /*  Butterfly process for the i0+3fftLen/4 sample */

#ifndef ARM_MATH_BIG_ENDIAN

                out1 = __SMUAD(C3, R) >> 16u;
                out2 = __SMUSDX(C3, R);

#else

                out1 = __SMUSDX(R, C3) >> 16u;
                out2 = __SMUAD(C3, R);

#endif /*      #ifndef ARM_MATH_BIG_ENDIAN     */

                /* xd' = (xa-yb-xc+yd)* co3 + (ya+xb-yc-xd)* (si3) */
                /* yd' = (ya+xb-yc-xd)* co3 - (xa-yb-xc+yd)* (si3) */
                _SIMD32_OFFSET(pSi3) =
                    ((out2) & 0xFFFF0000) | (out1 & 0x0000FFFF);
                pSi3 += 2 * n1;
            }
        }
        /*  Twiddle coefficients index modifier */
        twidCoefModifier <<= 2u;
    }
    /* end of middle stage process */


    /* data is in 10.6(q6) format for the 1024 point */
    /* data is in 8.8(q8) format for the 256 point */
    /* data is in 6.10(q10) format for the 64 point */
    /* data is in 4.12(q12) format for the 16 point */

    /*  Initializations for the last stage */
    j = fftLen >> 2;

    ptr1 = &pSrc16[0];

    /* start of last stage process */

    /*  Butterfly implementation */
    do
    {
        /* Read xa (real), ya(imag) input */
        xaya = *__SIMD32(ptr1)++;

        /* Read xb (real), yb(imag) input */
        xbyb = *__SIMD32(ptr1)++;

        /* Read xc (real), yc(imag) input */
        xcyc = *__SIMD32(ptr1)++;

        /* Read xd (real), yd(imag) input */
        xdyd = *__SIMD32(ptr1)++;

        /* R = packed((ya + yc), (xa + xc)) */
        R = __QADD16(xaya, xcyc);

        /* T = packed((yb + yd), (xb + xd)) */
        T = __QADD16(xbyb, xdyd);

        /* pointer updation for writing */
        ptr1 = ptr1 - 8u;


        /* xa' = xa + xb + xc + xd */
        /* ya' = ya + yb + yc + yd */
        *__SIMD32(ptr1)++ = __SHADD16(R, T);

        /* T = packed((yb + yd), (xb + xd)) */
        T = __QADD16(xbyb, xdyd);

        /* xc' = (xa-xb+xc-xd) */
        /* yc' = (ya-yb+yc-yd) */
        *__SIMD32(ptr1)++ = __SHSUB16(R, T);

        /* S = packed((ya - yc), (xa - xc)) */
        S = __QSUB16(xaya, xcyc);

        /* Read yd (real), xd(imag) input */
        /* T = packed( (yb - yd), (xb - xd))  */
        U = __QSUB16(xbyb, xdyd);

#ifndef ARM_MATH_BIG_ENDIAN

        /* xb' = (xa+yb-xc-yd) */
        /* yb' = (ya-xb-yc+xd) */
        *__SIMD32(ptr1)++ = __SHSAX(S, U);


        /* xd' = (xa-yb-xc+yd) */
        /* yd' = (ya+xb-yc-xd) */
        *__SIMD32(ptr1)++ = __SHASX(S, U);

#else

        /* xb' = (xa+yb-xc-yd) */
        /* yb' = (ya-xb-yc+xd) */
        *__SIMD32(ptr1)++ = __SHASX(S, U);


        /* xd' = (xa-yb-xc+yd) */
        /* yd' = (ya+xb-yc-xd) */
        *__SIMD32(ptr1)++ = __SHSAX(S, U);

#endif /*      #ifndef ARM_MATH_BIG_ENDIAN     */

    }
    while(--j);

    /* end of last stage process */

    /* output is in 11.5(q5) format for the 1024 point */
    /* output is in 9.7(q7) format for the 256 point   */
    /* output is in 7.9(q9) format for the 64 point  */
    /* output is in 5.11(q11) format for the 16 point  */


#else

    /* Run the below code for Cortex-M0 */

    q15_t R0, R1, S0, S1, T0, T1, U0, U1;
    q15_t Co1, Si1, Co2, Si2, Co3, Si3, out1, out2;
    uint32_t n1, n2, ic, i0, i1, i2, i3, j, k;

    /* Total process is divided into three stages */

    /* process first stage, middle stages, & last stage */

    /*  Initializations for the first stage */
    n2 = fftLen;
    n1 = n2;

    /* n2 = fftLen/4 */
    n2 >>= 2u;

    /* Index for twiddle coefficient */
    ic = 0u;

    /* Index for input read and output write */
    i0 = 0u;
    j = n2;

    /* Input is in 1.15(q15) format */

    /*  start of first stage process */
    do
    {
        /*  Butterfly implementation */

        /*  index calculation for the input as, */
        /*  pSrc16[i0 + 0], pSrc16[i0 + fftLen/4], pSrc16[i0 + fftLen/2], pSrc16[i0 + 3fftLen/4] */
        i1 = i0 + n2;
        i2 = i1 + n2;
        i3 = i2 + n2;

        /*  Reading i0, i0+fftLen/2 inputs */

        /* input is down scale by 4 to avoid overflow */
        /* Read ya (real), xa(imag) input */
        T0 = pSrc16[i0 * 2u] >> 2u;
        T1 = pSrc16[(i0 * 2u) + 1u] >> 2u;

        /* input is down scale by 4 to avoid overflow */
        /* Read yc (real), xc(imag) input */
        S0 = pSrc16[i2 * 2u] >> 2u;
        S1 = pSrc16[(i2 * 2u) + 1u] >> 2u;

        /* R0 = (ya + yc) */
        R0 = __SSAT(T0 + S0, 16u);
        /* R1 = (xa + xc) */
        R1 = __SSAT(T1 + S1, 16u);

        /* S0 = (ya - yc) */
        S0 = __SSAT(T0 - S0, 16);
        /* S1 = (xa - xc) */
        S1 = __SSAT(T1 - S1, 16);

        /*  Reading i0+fftLen/4 , i0+3fftLen/4 inputs */
        /* input is down scale by 4 to avoid overflow */
        /* Read yb (real), xb(imag) input */
        T0 = pSrc16[i1 * 2u] >> 2u;
        T1 = pSrc16[(i1 * 2u) + 1u] >> 2u;

        /* input is down scale by 4 to avoid overflow */
        /* Read yd (real), xd(imag) input */
        U0 = pSrc16[i3 * 2u] >> 2u;
        U1 = pSrc16[(i3 * 2u) + 1] >> 2u;

        /* T0 = (yb + yd) */
        T0 = __SSAT(T0 + U0, 16u);
        /* T1 = (xb + xd) */
        T1 = __SSAT(T1 + U1, 16u);

        /*  writing the butterfly processed i0 sample */
        /* ya' = ya + yb + yc + yd */
        /* xa' = xa + xb + xc + xd */
        pSrc16[i0 * 2u] = (R0 >> 1u) + (T0 >> 1u);
        pSrc16[(i0 * 2u) + 1u] = (R1 >> 1u) + (T1 >> 1u);

        /* R0 = (ya + yc) - (yb + yd) */
        /* R1 = (xa + xc) - (xb + xd) */
        R0 = __SSAT(R0 - T0, 16u);
        R1 = __SSAT(R1 - T1, 16u);

        /* co2 & si2 are read from Coefficient pointer */
        Co2 = pCoef16[2u * ic * 2u];
        Si2 = pCoef16[(2u * ic * 2u) + 1];

        /* xc' = (xa-xb+xc-xd)* co2 + (ya-yb+yc-yd)* (si2) */
        out1 = (q15_t) ((Co2 * R0 + Si2 * R1) >> 16u);
        /* yc' = (ya-yb+yc-yd)* co2 - (xa-xb+xc-xd)* (si2) */
        out2 = (q15_t) ((-Si2 * R0 + Co2 * R1) >> 16u);

        /*  Reading i0+fftLen/4 */
        /* input is down scale by 4 to avoid overflow */
        /* T0 = yb, T1 =  xb */
        T0 = pSrc16[i1 * 2u] >> 2;
        T1 = pSrc16[(i1 * 2u) + 1] >> 2;

        /* writing the butterfly processed i0 + fftLen/4 sample */
        /* writing output(xc', yc') in little endian format */
        pSrc16[i1 * 2u] = out1;
        pSrc16[(i1 * 2u) + 1] = out2;

        /*  Butterfly calculations */
        /* input is down scale by 4 to avoid overflow */
        /* U0 = yd, U1 = xd */
        U0 = pSrc16[i3 * 2u] >> 2;
        U1 = pSrc16[(i3 * 2u) + 1] >> 2;
        /* T0 = yb-yd */
        T0 = __SSAT(T0 - U0, 16);
        /* T1 = xb-xd */
        T1 = __SSAT(T1 - U1, 16);

        /* R1 = (ya-yc) + (xb- xd),  R0 = (xa-xc) - (yb-yd)) */
        R0 = (q15_t) __SSAT((q31_t) (S0 - T1), 16);
        R1 = (q15_t) __SSAT((q31_t) (S1 + T0), 16);

        /* S1 = (ya-yc) - (xb- xd), S0 = (xa-xc) + (yb-yd)) */
        S0 = (q15_t) __SSAT(((q31_t) S0 + T1), 16u);
        S1 = (q15_t) __SSAT(((q31_t) S1 - T0), 16u);

        /* co1 & si1 are read from Coefficient pointer */
        Co1 = pCoef16[ic * 2u];
        Si1 = pCoef16[(ic * 2u) + 1];
        /*  Butterfly process for the i0+fftLen/2 sample */
        /* xb' = (xa+yb-xc-yd)* co1 + (ya-xb-yc+xd)* (si1) */
        out1 = (q15_t) ((Si1 * S1 + Co1 * S0) >> 16);
        /* yb' = (ya-xb-yc+xd)* co1 - (xa+yb-xc-yd)* (si1) */
        out2 = (q15_t) ((-Si1 * S0 + Co1 * S1) >> 16);

        /* writing output(xb', yb') in little endian format */
        pSrc16[i2 * 2u] = out1;
        pSrc16[(i2 * 2u) + 1] = out2;

        /* Co3 & si3 are read from Coefficient pointer */
        Co3 = pCoef16[3u * (ic * 2u)];
        Si3 = pCoef16[(3u * (ic * 2u)) + 1];
        /*  Butterfly process for the i0+3fftLen/4 sample */
        /* xd' = (xa-yb-xc+yd)* Co3 + (ya+xb-yc-xd)* (si3) */
        out1 = (q15_t) ((Si3 * R1 + Co3 * R0) >> 16u);
        /* yd' = (ya+xb-yc-xd)* Co3 - (xa-yb-xc+yd)* (si3) */
        out2 = (q15_t) ((-Si3 * R0 + Co3 * R1) >> 16u);
        /* writing output(xd', yd') in little endian format */
        pSrc16[i3 * 2u] = out1;
        pSrc16[(i3 * 2u) + 1] = out2;

        /*  Twiddle coefficients index modifier */
        ic = ic + twidCoefModifier;

        /*  Updating input index */
        i0 = i0 + 1u;

    }
    while(--j);
    /* data is in 4.11(q11) format */

    /* end of first stage process */


    /* start of middle stage process */

    /*  Twiddle coefficients index modifier */
    twidCoefModifier <<= 2u;

    /*  Calculation of Middle stage */
    for (k = fftLen / 4u; k > 4u; k >>= 2u)
    {
        /*  Initializations for the middle stage */
        n1 = n2;
        n2 >>= 2u;
        ic = 0u;

        for (j = 0u; j <= (n2 - 1u); j++)
        {
            /*  index calculation for the coefficients */
            Co1 = pCoef16[ic * 2u];
            Si1 = pCoef16[(ic * 2u) + 1u];
            Co2 = pCoef16[2u * (ic * 2u)];
            Si2 = pCoef16[(2u * (ic * 2u)) + 1u];
            Co3 = pCoef16[3u * (ic * 2u)];
            Si3 = pCoef16[(3u * (ic * 2u)) + 1u];

            /*  Twiddle coefficients index modifier */
            ic = ic + twidCoefModifier;

            /*  Butterfly implementation */
            for (i0 = j; i0 < fftLen; i0 += n1)
            {
                /*  index calculation for the input as, */
                /*  pSrc16[i0 + 0], pSrc16[i0 + fftLen/4], pSrc16[i0 + fftLen/2], pSrc16[i0 + 3fftLen/4] */
                i1 = i0 + n2;
                i2 = i1 + n2;
                i3 = i2 + n2;

                /*  Reading i0, i0+fftLen/2 inputs */
                /* Read ya (real), xa(imag) input */
                T0 = pSrc16[i0 * 2u];
                T1 = pSrc16[(i0 * 2u) + 1u];

                /* Read yc (real), xc(imag) input */
                S0 = pSrc16[i2 * 2u];
                S1 = pSrc16[(i2 * 2u) + 1u];

                /* R0 = (ya + yc), R1 = (xa + xc) */
                R0 = __SSAT(T0 + S0, 16);
                R1 = __SSAT(T1 + S1, 16);

                /* S0 = (ya - yc), S1 =(xa - xc) */
                S0 = __SSAT(T0 - S0, 16);
                S1 = __SSAT(T1 - S1, 16);

                /*  Reading i0+fftLen/4 , i0+3fftLen/4 inputs */
                /* Read yb (real), xb(imag) input */
                T0 = pSrc16[i1 * 2u];
                T1 = pSrc16[(i1 * 2u) + 1u];

                /* Read yd (real), xd(imag) input */
                U0 = pSrc16[i3 * 2u];
                U1 = pSrc16[(i3 * 2u) + 1u];


                /* T0 = (yb + yd), T1 = (xb + xd) */
                T0 = __SSAT(T0 + U0, 16);
                T1 = __SSAT(T1 + U1, 16);

                /*  writing the butterfly processed i0 sample */

                /* xa' = xa + xb + xc + xd */
                /* ya' = ya + yb + yc + yd */
                out1 = ((R0 >> 1u) + (T0 >> 1u)) >> 1u;
                out2 = ((R1 >> 1u) + (T1 >> 1u)) >> 1u;

                pSrc16[i0 * 2u] = out1;
                pSrc16[(2u * i0) + 1u] = out2;

                /* R0 = (ya + yc) - (yb + yd), R1 = (xa + xc) - (xb + xd) */
                R0 = (R0 >> 1u) - (T0 >> 1u);
                R1 = (R1 >> 1u) - (T1 >> 1u);

                /* (ya-yb+yc-yd)* (si2) + (xa-xb+xc-xd)* co2 */
                out1 = (q15_t) ((Co2 * R0 + Si2 * R1) >> 16u);

                /* (ya-yb+yc-yd)* co2 - (xa-xb+xc-xd)* (si2) */
                out2 = (q15_t) ((-Si2 * R0 + Co2 * R1) >> 16u);

                /*  Reading i0+3fftLen/4 */
                /* Read yb (real), xb(imag) input */
                T0 = pSrc16[i1 * 2u];
                T1 = pSrc16[(i1 * 2u) + 1u];

                /*  writing the butterfly processed i0 + fftLen/4 sample */
                /* xc' = (xa-xb+xc-xd)* co2 + (ya-yb+yc-yd)* (si2) */
                /* yc' = (ya-yb+yc-yd)* co2 - (xa-xb+xc-xd)* (si2) */
                pSrc16[i1 * 2u] = out1;
                pSrc16[(i1 * 2u) + 1u] = out2;

                /*  Butterfly calculations */

                /* Read yd (real), xd(imag) input */
                U0 = pSrc16[i3 * 2u];
                U1 = pSrc16[(i3 * 2u) + 1u];

                /* T0 = yb-yd, T1 = xb-xd */
                T0 = __SSAT(T0 - U0, 16);
                T1 = __SSAT(T1 - U1, 16);

                /* R0 = (ya-yc) + (xb- xd), R1 = (xa-xc) - (yb-yd)) */
                R0 = (S0 >> 1u) - (T1 >> 1u);
                R1 = (S1 >> 1u) + (T0 >> 1u);

                /* S0 = (ya-yc) - (xb- xd), S1 = (xa-xc) + (yb-yd)) */
                S0 = (S0 >> 1u) + (T1 >> 1u);
                S1 = (S1 >> 1u) - (T0 >> 1u);

                /*  Butterfly process for the i0+fftLen/2 sample */
                out1 = (q15_t) ((Co1 * S0 + Si1 * S1) >> 16u);

                out2 = (q15_t) ((-Si1 * S0 + Co1 * S1) >> 16u);

                /* xb' = (xa+yb-xc-yd)* co1 + (ya-xb-yc+xd)* (si1) */
                /* yb' = (ya-xb-yc+xd)* co1 - (xa+yb-xc-yd)* (si1) */
                pSrc16[i2 * 2u] = out1;
                pSrc16[(i2 * 2u) + 1u] = out2;

                /*  Butterfly process for the i0+3fftLen/4 sample */
                out1 = (q15_t) ((Si3 * R1 + Co3 * R0) >> 16u);

                out2 = (q15_t) ((-Si3 * R0 + Co3 * R1) >> 16u);
                /* xd' = (xa-yb-xc+yd)* Co3 + (ya+xb-yc-xd)* (si3) */
                /* yd' = (ya+xb-yc-xd)* Co3 - (xa-yb-xc+yd)* (si3) */
                pSrc16[i3 * 2u] = out1;
                pSrc16[(i3 * 2u) + 1u] = out2;
            }
        }
        /*  Twiddle coefficients index modifier */
        twidCoefModifier <<= 2u;
    }
    /* end of middle stage process */


    /* data is in 10.6(q6) format for the 1024 point */
    /* data is in 8.8(q8) format for the 256 point */
    /* data is in 6.10(q10) format for the 64 point */
    /* data is in 4.12(q12) format for the 16 point */

    /*  Initializations for the last stage */
    n1 = n2;
    n2 >>= 2u;

    /* start of last stage process */

    /*  Butterfly implementation */
    for (i0 = 0u; i0 <= (fftLen - n1); i0 += n1)
    {
        /*  index calculation for the input as, */
        /*  pSrc16[i0 + 0], pSrc16[i0 + fftLen/4], pSrc16[i0 + fftLen/2], pSrc16[i0 + 3fftLen/4] */
        i1 = i0 + n2;
        i2 = i1 + n2;
        i3 = i2 + n2;

        /*  Reading i0, i0+fftLen/2 inputs */
        /* Read ya (real), xa(imag) input */
        T0 = pSrc16[i0 * 2u];
        T1 = pSrc16[(i0 * 2u) + 1u];

        /* Read yc (real), xc(imag) input */
        S0 = pSrc16[i2 * 2u];
        S1 = pSrc16[(i2 * 2u) + 1u];

        /* R0 = (ya + yc), R1 = (xa + xc) */
        R0 = __SSAT(T0 + S0, 16u);
        R1 = __SSAT(T1 + S1, 16u);

        /* S0 = (ya - yc), S1 = (xa - xc) */
        S0 = __SSAT(T0 - S0, 16u);
        S1 = __SSAT(T1 - S1, 16u);

        /*  Reading i0+fftLen/4 , i0+3fftLen/4 inputs */
        /* Read yb (real), xb(imag) input */
        T0 = pSrc16[i1 * 2u];
        T1 = pSrc16[(i1 * 2u) + 1u];
        /* Read yd (real), xd(imag) input */
        U0 = pSrc16[i3 * 2u];
        U1 = pSrc16[(i3 * 2u) + 1u];

        /* T0 = (yb + yd), T1 = (xb + xd)) */
        T0 = __SSAT(T0 + U0, 16u);
        T1 = __SSAT(T1 + U1, 16u);

        /*  writing the butterfly processed i0 sample */
        /* xa' = xa + xb + xc + xd */
        /* ya' = ya + yb + yc + yd */
        pSrc16[i0 * 2u] = (R0 >> 1u) + (T0 >> 1u);
        pSrc16[(i0 * 2u) + 1u] = (R1 >> 1u) + (T1 >> 1u);

        /* R0 = (ya + yc) - (yb + yd), R1 = (xa + xc) - (xb + xd) */
        R0 = (R0 >> 1u) - (T0 >> 1u);
        R1 = (R1 >> 1u) - (T1 >> 1u);
        /* Read yb (real), xb(imag) input */
        T0 = pSrc16[i1 * 2u];
        T1 = pSrc16[(i1 * 2u) + 1u];

        /*  writing the butterfly processed i0 + fftLen/4 sample */
        /* xc' = (xa-xb+xc-xd) */
        /* yc' = (ya-yb+yc-yd) */
        pSrc16[i1 * 2u] = R0;
        pSrc16[(i1 * 2u) + 1u] = R1;

        /* Read yd (real), xd(imag) input */
        U0 = pSrc16[i3 * 2u];
        U1 = pSrc16[(i3 * 2u) + 1u];
        /* T0 = (yb - yd), T1 = (xb - xd)  */
        T0 = __SSAT(T0 - U0, 16u);
        T1 = __SSAT(T1 - U1, 16u);

        /*  writing the butterfly processed i0 + fftLen/2 sample */
        /* xb' = (xa+yb-xc-yd) */
        /* yb' = (ya-xb-yc+xd) */
        pSrc16[i2 * 2u] = (S0 >> 1u) + (T1 >> 1u);
        pSrc16[(i2 * 2u) + 1u] = (S1 >> 1u) - (T0 >> 1u);

        /*  writing the butterfly processed i0 + 3fftLen/4 sample */
        /* xd' = (xa-yb-xc+yd) */
        /* yd' = (ya+xb-yc-xd) */
        pSrc16[i3 * 2u] = (S0 >> 1u) - (T1 >> 1u);
        pSrc16[(i3 * 2u) + 1u] = (S1 >> 1u) + (T0 >> 1u);

    }

    /* end of last stage process */

    /* output is in 11.5(q5) format for the 1024 point */
    /* output is in 9.7(q7) format for the 256 point   */
    /* output is in 7.9(q9) format for the 64 point  */
    /* output is in 5.11(q11) format for the 16 point  */

#endif /* #ifndef ARM_MATH_CM0_FAMILY */

}


/**
 * @brief  Core function for the Q15 CIFFT butterfly process.
 * @param[in, out] *pSrc16          points to the in-place buffer of Q15 data type.
 * @param[in]      fftLen           length of the FFT.
 * @param[in]      *pCoef16         points to twiddle coefficient buffer.
 * @param[in]      twidCoefModifier twiddle coefficient modifier that supports different size FFTs with the same twiddle factor table.
 * @return none.
 */

/*
* Radix-4 IFFT algorithm used is :
*
* CIFFT uses same twiddle coefficients as CFFT function
*  x[k] = x[n] + (j)k * x[n + fftLen/4] + (-1)k * x[n+fftLen/2] + (-j)k * x[n+3*fftLen/4]
*
*
* IFFT is implemented with following changes in equations from FFT
*
* Input real and imaginary data:
* x(n) = xa + j * ya
* x(n+N/4 ) = xb + j * yb
* x(n+N/2 ) = xc + j * yc
* x(n+3N 4) = xd + j * yd
*
*
* Output real and imaginary data:
* x(4r) = xa'+ j * ya'
* x(4r+1) = xb'+ j * yb'
* x(4r+2) = xc'+ j * yc'
* x(4r+3) = xd'+ j * yd'
*
*
* Twiddle factors for radix-4 IFFT:
* Wn = co1 + j * (si1)
* W2n = co2 + j * (si2)
* W3n = co3 + j * (si3)

* The real and imaginary output values for the radix-4 butterfly are
* xa' = xa + xb + xc + xd
* ya' = ya + yb + yc + yd
* xb' = (xa-yb-xc+yd)* co1 - (ya+xb-yc-xd)* (si1)
* yb' = (ya+xb-yc-xd)* co1 + (xa-yb-xc+yd)* (si1)
* xc' = (xa-xb+xc-xd)* co2 - (ya-yb+yc-yd)* (si2)
* yc' = (ya-yb+yc-yd)* co2 + (xa-xb+xc-xd)* (si2)
* xd' = (xa+yb-xc-yd)* co3 - (ya-xb-yc+xd)* (si3)
* yd' = (ya-xb-yc+xd)* co3 + (xa+yb-xc-yd)* (si3)
*
*/

void arm_radix4_butterfly_inverse_q15(
    q15_t *pSrc16,
    uint32_t fftLen,
    q15_t *pCoef16,
    uint32_t twidCoefModifier)
{

#ifndef ARM_MATH_CM0_FAMILY

    /* Run the below code for Cortex-M4 and Cortex-M3 */

    q31_t R, S, T, U;
    q31_t C1, C2, C3, out1, out2;
    uint32_t n1, n2, ic, i0, j, k;

    q15_t *ptr1;
    q15_t *pSi0;
    q15_t *pSi1;
    q15_t *pSi2;
    q15_t *pSi3;

    q31_t xaya, xbyb, xcyc, xdyd;

    /* Total process is divided into three stages */

    /* process first stage, middle stages, & last stage */

    /*  Initializations for the first stage */
    n2 = fftLen;
    n1 = n2;

    /* n2 = fftLen/4 */
    n2 >>= 2u;

    /* Index for twiddle coefficient */
    ic = 0u;

    /* Index for input read and output write */
    j = n2;

    pSi0 = pSrc16;
    pSi1 = pSi0 + 2 * n2;
    pSi2 = pSi1 + 2 * n2;
    pSi3 = pSi2 + 2 * n2;

    /* Input is in 1.15(q15) format */

    /*  start of first stage process */
    do
    {
        /*  Butterfly implementation */

        /*  Reading i0, i0+fftLen/2 inputs */
        /* Read ya (real), xa(imag) input */
        T = _SIMD32_OFFSET(pSi0);
        T = __SHADD16(T, 0);
        T = __SHADD16(T, 0);

        /* Read yc (real), xc(imag) input */
        S = _SIMD32_OFFSET(pSi2);
        S = __SHADD16(S, 0);
        S = __SHADD16(S, 0);

        /* R = packed((ya + yc), (xa + xc) ) */
        R = __QADD16(T, S);

        /* S = packed((ya - yc), (xa - xc) ) */
        S = __QSUB16(T, S);

        /*  Reading i0+fftLen/4 , i0+3fftLen/4 inputs */
        /* Read yb (real), xb(imag) input */
        T = _SIMD32_OFFSET(pSi1);
        T = __SHADD16(T, 0);
        T = __SHADD16(T, 0);

        /* Read yd (real), xd(imag) input */
        U = _SIMD32_OFFSET(pSi3);
        U = __SHADD16(U, 0);
        U = __SHADD16(U, 0);

        /* T = packed((yb + yd), (xb + xd) ) */
        T = __QADD16(T, U);

        /*  writing the butterfly processed i0 sample */
        /* xa' = xa + xb + xc + xd */
        /* ya' = ya + yb + yc + yd */
        _SIMD32_OFFSET(pSi0) = __SHADD16(R, T);
        pSi0 += 2;

        /* R = packed((ya + yc) - (yb + yd), (xa + xc)- (xb + xd)) */
        R = __QSUB16(R, T);

        /* co2 & si2 are read from SIMD Coefficient pointer */
        C2 = _SIMD32_OFFSET(pCoef16 + (4u * ic));

#ifndef ARM_MATH_BIG_ENDIAN

        /* xc' = (xa-xb+xc-xd)* co2 + (ya-yb+yc-yd)* (si2) */
        out1 = __SMUSD(C2, R) >> 16u;
        /* yc' = (ya-yb+yc-yd)* co2 - (xa-xb+xc-xd)* (si2) */
        out2 = __SMUADX(C2, R);

#else

        /* xc' = (ya-yb+yc-yd)* co2 - (xa-xb+xc-xd)* (si2) */
        out1 = __SMUADX(C2, R) >> 16u;
        /* yc' = (xa-xb+xc-xd)* co2 + (ya-yb+yc-yd)* (si2) */
        out2 = __SMUSD(__QSUB16(0, C2), R);

#endif /*      #ifndef ARM_MATH_BIG_ENDIAN     */

        /*  Reading i0+fftLen/4 */
        /* T = packed(yb, xb) */
        T = _SIMD32_OFFSET(pSi1);
        T = __SHADD16(T, 0);
        T = __SHADD16(T, 0);

        /* writing the butterfly processed i0 + fftLen/4 sample */
        /* writing output(xc', yc') in little endian format */
        _SIMD32_OFFSET(pSi1) =
            (q31_t) ((out2) & 0xFFFF0000) | (out1 & 0x0000FFFF);
        pSi1 += 2;

        /*  Butterfly calculations */
        /* U = packed(yd, xd) */
        U = _SIMD32_OFFSET(pSi3);
        U = __SHADD16(U, 0);
        U = __SHADD16(U, 0);

        /* T = packed(yb-yd, xb-xd) */
        T = __QSUB16(T, U);

#ifndef ARM_MATH_BIG_ENDIAN

        /* R = packed((ya-yc) + (xb- xd) , (xa-xc) - (yb-yd)) */
        R = __QSAX(S, T);
        /* S = packed((ya-yc) + (xb- xd),  (xa-xc) - (yb-yd)) */
        S = __QASX(S, T);

#else

        /* R = packed((ya-yc) + (xb- xd) , (xa-xc) - (yb-yd)) */
        R = __QASX(S, T);
        /* S = packed((ya-yc) - (xb- xd),  (xa-xc) + (yb-yd)) */
        S = __QSAX(S, T);

#endif /*      #ifndef ARM_MATH_BIG_ENDIAN     */

        /* co1 & si1 are read from SIMD Coefficient pointer */
        C1 = _SIMD32_OFFSET(pCoef16 + (2u * ic));
        /*  Butterfly process for the i0+fftLen/2 sample */

#ifndef ARM_MATH_BIG_ENDIAN

        /* xb' = (xa+yb-xc-yd)* co1 + (ya-xb-yc+xd)* (si1) */
        out1 = __SMUSD(C1, S) >> 16u;
        /* yb' = (ya-xb-yc+xd)* co1 - (xa+yb-xc-yd)* (si1) */
        out2 = __SMUADX(C1, S);

#else

        /* xb' = (ya-xb-yc+xd)* co1 - (xa+yb-xc-yd)* (si1) */
        out1 = __SMUADX(C1, S) >> 16u;
        /* yb' = (xa+yb-xc-yd)* co1 + (ya-xb-yc+xd)* (si1) */
        out2 = __SMUSD(__QSUB16(0, C1), S);

#endif /*      #ifndef ARM_MATH_BIG_ENDIAN     */

        /* writing output(xb', yb') in little endian format */
        _SIMD32_OFFSET(pSi2) =
            ((out2) & 0xFFFF0000) | ((out1) & 0x0000FFFF);
        pSi2 += 2;


        /* co3 & si3 are read from SIMD Coefficient pointer */
        C3 = _SIMD32_OFFSET(pCoef16 + (6u * ic));
        /*  Butterfly process for the i0+3fftLen/4 sample */

#ifndef ARM_MATH_BIG_ENDIAN

        /* xd' = (xa-yb-xc+yd)* co3 + (ya+xb-yc-xd)* (si3) */
        out1 = __SMUSD(C3, R) >> 16u;
        /* yd' = (ya+xb-yc-xd)* co3 - (xa-yb-xc+yd)* (si3) */
        out2 = __SMUADX(C3, R);

#else

        /* xd' = (ya+xb-yc-xd)* co3 - (xa-yb-xc+yd)* (si3) */
        out1 = __SMUADX(C3, R) >> 16u;
        /* yd' = (xa-yb-xc+yd)* co3 + (ya+xb-yc-xd)* (si3) */
        out2 = __SMUSD(__QSUB16(0, C3), R);

#endif /*      #ifndef ARM_MATH_BIG_ENDIAN     */

        /* writing output(xd', yd') in little endian format */
        _SIMD32_OFFSET(pSi3) =
            ((out2) & 0xFFFF0000) | (out1 & 0x0000FFFF);
        pSi3 += 2;

        /*  Twiddle coefficients index modifier */
        ic = ic + twidCoefModifier;

    }
    while(--j);
    /* data is in 4.11(q11) format */

    /* end of first stage process */


    /* start of middle stage process */

    /*  Twiddle coefficients index modifier */
    twidCoefModifier <<= 2u;

    /*  Calculation of Middle stage */
    for (k = fftLen / 4u; k > 4u; k >>= 2u)
    {
        /*  Initializations for the middle stage */
        n1 = n2;
        n2 >>= 2u;
        ic = 0u;

        for (j = 0u; j <= (n2 - 1u); j++)
        {
            /*  index calculation for the coefficients */
            C1 = _SIMD32_OFFSET(pCoef16 + (2u * ic));
            C2 = _SIMD32_OFFSET(pCoef16 + (4u * ic));
            C3 = _SIMD32_OFFSET(pCoef16 + (6u * ic));

            /*  Twiddle coefficients index modifier */
            ic = ic + twidCoefModifier;

            pSi0 = pSrc16 + 2 * j;
            pSi1 = pSi0 + 2 * n2;
            pSi2 = pSi1 + 2 * n2;
            pSi3 = pSi2 + 2 * n2;

            /*  Butterfly implementation */
            for (i0 = j; i0 < fftLen; i0 += n1)
            {
                /*  Reading i0, i0+fftLen/2 inputs */
                /* Read ya (real), xa(imag) input */
                T = _SIMD32_OFFSET(pSi0);

                /* Read yc (real), xc(imag) input */
                S = _SIMD32_OFFSET(pSi2);

                /* R = packed( (ya + yc), (xa + xc)) */
                R = __QADD16(T, S);

                /* S = packed((ya - yc), (xa - xc)) */
                S = __QSUB16(T, S);

                /*  Reading i0+fftLen/4 , i0+3fftLen/4 inputs */
                /* Read yb (real), xb(imag) input */
                T = _SIMD32_OFFSET(pSi1);

                /* Read yd (real), xd(imag) input */
                U = _SIMD32_OFFSET(pSi3);

                /* T = packed( (yb + yd), (xb + xd)) */
                T = __QADD16(T, U);

                /*  writing the butterfly processed i0 sample */

                /* xa' = xa + xb + xc + xd */
                /* ya' = ya + yb + yc + yd */
                out1 = __SHADD16(R, T);
                out1 = __SHADD16(out1, 0);
                _SIMD32_OFFSET(pSi0) = out1;
                pSi0 += 2 * n1;

                /* R = packed( (ya + yc) - (yb + yd), (xa + xc) - (xb + xd)) */
                R = __SHSUB16(R, T);

#ifndef ARM_MATH_BIG_ENDIAN

                /* (ya-yb+yc-yd)* (si2) + (xa-xb+xc-xd)* co2 */
                out1 = __SMUSD(C2, R) >> 16u;

                /* (ya-yb+yc-yd)* co2 - (xa-xb+xc-xd)* (si2) */
                out2 = __SMUADX(C2, R);

#else

                /* (ya-yb+yc-yd)* co2 - (xa-xb+xc-xd)* (si2) */
                out1 = __SMUADX(R, C2) >> 16u;

                /* (ya-yb+yc-yd)* (si2) + (xa-xb+xc-xd)* co2 */
                out2 = __SMUSD(__QSUB16(0, C2), R);

#endif /*      #ifndef ARM_MATH_BIG_ENDIAN     */

                /*  Reading i0+3fftLen/4 */
                /* Read yb (real), xb(imag) input */
                T = _SIMD32_OFFSET(pSi1);

                /*  writing the butterfly processed i0 + fftLen/4 sample */
                /* xc' = (xa-xb+xc-xd)* co2 + (ya-yb+yc-yd)* (si2) */
                /* yc' = (ya-yb+yc-yd)* co2 - (xa-xb+xc-xd)* (si2) */
                _SIMD32_OFFSET(pSi1) =
                    ((out2) & 0xFFFF0000) | (out1 & 0x0000FFFF);
                pSi1 += 2 * n1;

                /*  Butterfly calculations */

                /* Read yd (real), xd(imag) input */
                U = _SIMD32_OFFSET(pSi3);

                /* T = packed(yb-yd, xb-xd) */
                T = __QSUB16(T, U);

#ifndef ARM_MATH_BIG_ENDIAN

                /* R = packed((ya-yc) + (xb- xd) , (xa-xc) - (yb-yd)) */
                R = __SHSAX(S, T);

                /* S = packed((ya-yc) - (xb- xd),  (xa-xc) + (yb-yd)) */
                S = __SHASX(S, T);


                /*  Butterfly process for the i0+fftLen/2 sample */
                out1 = __SMUSD(C1, S) >> 16u;
                out2 = __SMUADX(C1, S);

#else

                /* R = packed((ya-yc) + (xb- xd) , (xa-xc) - (yb-yd)) */
                R = __SHASX(S, T);

                /* S = packed((ya-yc) - (xb- xd),  (xa-xc) + (yb-yd)) */
                S = __SHSAX(S, T);


                /*  Butterfly process for the i0+fftLen/2 sample */
                out1 = __SMUADX(S, C1) >> 16u;
                out2 = __SMUSD(__QSUB16(0, C1), S);

#endif /*      #ifndef ARM_MATH_BIG_ENDIAN     */

                /* xb' = (xa+yb-xc-yd)* co1 + (ya-xb-yc+xd)* (si1) */
                /* yb' = (ya-xb-yc+xd)* co1 - (xa+yb-xc-yd)* (si1) */
                _SIMD32_OFFSET(pSi2) =
                    ((out2) & 0xFFFF0000) | (out1 & 0x0000FFFF);
                pSi2 += 2 * n1;

                /*  Butterfly process for the i0+3fftLen/4 sample */

#ifndef ARM_MATH_BIG_ENDIAN

                out1 = __SMUSD(C3, R) >> 16u;
                out2 = __SMUADX(C3, R);

#else

                out1 = __SMUADX(C3, R) >> 16u;
                out2 = __SMUSD(__QSUB16(0, C3), R);

#endif /*      #ifndef ARM_MATH_BIG_ENDIAN     */

                /* xd' = (xa-yb-xc+yd)* co3 + (ya+xb-yc-xd)* (si3) */
                /* yd' = (ya+xb-yc-xd)* co3 - (xa-yb-xc+yd)* (si3) */
                _SIMD32_OFFSET(pSi3) =
                    ((out2) & 0xFFFF0000) | (out1 & 0x0000FFFF);
                pSi3 += 2 * n1;
            }
        }
        /*  Twiddle coefficients index modifier */
        twidCoefModifier <<= 2u;
    }
    /* end of middle stage process */

    /* data is in 10.6(q6) format for the 1024 point */
    /* data is in 8.8(q8) format for the 256 point */
    /* data is in 6.10(q10) format for the 64 point */
    /* data is in 4.12(q12) format for the 16 point */

    /*  Initializations for the last stage */
    j = fftLen >> 2;

    ptr1 = &pSrc16[0];

    /* start of last stage process */

    /*  Butterfly implementation */
    do
    {
        /* Read xa (real), ya(imag) input */
        xaya = *__SIMD32(ptr1)++;

        /* Read xb (real), yb(imag) input */
        xbyb = *__SIMD32(ptr1)++;

        /* Read xc (real), yc(imag) input */
        xcyc = *__SIMD32(ptr1)++;

        /* Read xd (real), yd(imag) input */
        xdyd = *__SIMD32(ptr1)++;

        /* R = packed((ya + yc), (xa + xc)) */
        R = __QADD16(xaya, xcyc);

        /* T = packed((yb + yd), (xb + xd)) */
        T = __QADD16(xbyb, xdyd);

        /* pointer updation for writing */
        ptr1 = ptr1 - 8u;


        /* xa' = xa + xb + xc + xd */
        /* ya' = ya + yb + yc + yd */
        *__SIMD32(ptr1)++ = __SHADD16(R, T);

        /* T = packed((yb + yd), (xb + xd)) */
        T = __QADD16(xbyb, xdyd);

        /* xc' = (xa-xb+xc-xd) */
        /* yc' = (ya-yb+yc-yd) */
        *__SIMD32(ptr1)++ = __SHSUB16(R, T);

        /* S = packed((ya - yc), (xa - xc)) */
        S = __QSUB16(xaya, xcyc);

        /* Read yd (real), xd(imag) input */
        /* T = packed( (yb - yd), (xb - xd))  */
        U = __QSUB16(xbyb, xdyd);

#ifndef ARM_MATH_BIG_ENDIAN

        /* xb' = (xa+yb-xc-yd) */
        /* yb' = (ya-xb-yc+xd) */
        *__SIMD32(ptr1)++ = __SHASX(S, U);


        /* xd' = (xa-yb-xc+yd) */
        /* yd' = (ya+xb-yc-xd) */
        *__SIMD32(ptr1)++ = __SHSAX(S, U);

#else

        /* xb' = (xa+yb-xc-yd) */
        /* yb' = (ya-xb-yc+xd) */
        *__SIMD32(ptr1)++ = __SHSAX(S, U);


        /* xd' = (xa-yb-xc+yd) */
        /* yd' = (ya+xb-yc-xd) */
        *__SIMD32(ptr1)++ = __SHASX(S, U);


#endif /*      #ifndef ARM_MATH_BIG_ENDIAN     */

    }
    while(--j);

    /* end of last stage  process */

    /* output is in 11.5(q5) format for the 1024 point */
    /* output is in 9.7(q7) format for the 256 point   */
    /* output is in 7.9(q9) format for the 64 point  */
    /* output is in 5.11(q11) format for the 16 point  */


#else

    /* Run the below code for Cortex-M0 */

    q15_t R0, R1, S0, S1, T0, T1, U0, U1;
    q15_t Co1, Si1, Co2, Si2, Co3, Si3, out1, out2;
    uint32_t n1, n2, ic, i0, i1, i2, i3, j, k;

    /* Total process is divided into three stages */

    /* process first stage, middle stages, & last stage */

    /*  Initializations for the first stage */
    n2 = fftLen;
    n1 = n2;

    /* n2 = fftLen/4 */
    n2 >>= 2u;

    /* Index for twiddle coefficient */
    ic = 0u;

    /* Index for input read and output write */
    i0 = 0u;

    j = n2;

    /* Input is in 1.15(q15) format */

    /*  Start of first stage process */
    do
    {
        /*  Butterfly implementation */

        /*  index calculation for the input as, */
        /*  pSrc16[i0 + 0], pSrc16[i0 + fftLen/4], pSrc16[i0 + fftLen/2], pSrc16[i0 + 3fftLen/4] */
        i1 = i0 + n2;
        i2 = i1 + n2;
        i3 = i2 + n2;

        /*  Reading i0, i0+fftLen/2 inputs */
        /* input is down scale by 4 to avoid overflow */
        /* Read ya (real), xa(imag) input */
        T0 = pSrc16[i0 * 2u] >> 2u;
        T1 = pSrc16[(i0 * 2u) + 1u] >> 2u;
        /* input is down scale by 4 to avoid overflow */
        /* Read yc (real), xc(imag) input */
        S0 = pSrc16[i2 * 2u] >> 2u;
        S1 = pSrc16[(i2 * 2u) + 1u] >> 2u;

        /* R0 = (ya + yc), R1 = (xa + xc) */
        R0 = __SSAT(T0 + S0, 16u);
        R1 = __SSAT(T1 + S1, 16u);
        /* S0 = (ya - yc), S1 = (xa - xc) */
        S0 = __SSAT(T0 - S0, 16u);
        S1 = __SSAT(T1 - S1, 16u);

        /*  Reading i0+fftLen/4 , i0+3fftLen/4 inputs */
        /* input is down scale by 4 to avoid overflow */
        /* Read yb (real), xb(imag) input */
        T0 = pSrc16[i1 * 2u] >> 2u;
        T1 = pSrc16[(i1 * 2u) + 1u] >> 2u;
        /* Read yd (real), xd(imag) input */
        /* input is down scale by 4 to avoid overflow */
        U0 = pSrc16[i3 * 2u] >> 2u;
        U1 = pSrc16[(i3 * 2u) + 1u] >> 2u;

        /* T0 = (yb + yd), T1 = (xb + xd) */
        T0 = __SSAT(T0 + U0, 16u);
        T1 = __SSAT(T1 + U1, 16u);

        /*  writing the butterfly processed i0 sample */
        /* xa' = xa + xb + xc + xd */
        /* ya' = ya + yb + yc + yd */
        pSrc16[i0 * 2u] = (R0 >> 1u) + (T0 >> 1u);
        pSrc16[(i0 * 2u) + 1u] = (R1 >> 1u) + (T1 >> 1u);

        /* R0 = (ya + yc) - (yb + yd), R1 = (xa + xc)- (xb + xd) */
        R0 = __SSAT(R0 - T0, 16u);
        R1 = __SSAT(R1 - T1, 16u);
        /* co2 & si2 are read from Coefficient pointer */
        Co2 = pCoef16[2u * ic * 2u];
        Si2 = pCoef16[(2u * ic * 2u) + 1u];
        /* xc' = (xa-xb+xc-xd)* co2 - (ya-yb+yc-yd)* (si2) */
        out1 = (q15_t) ((Co2 * R0 - Si2 * R1) >> 16u);
        /* yc' = (ya-yb+yc-yd)* co2 + (xa-xb+xc-xd)* (si2) */
        out2 = (q15_t) ((Si2 * R0 + Co2 * R1) >> 16u);

        /*  Reading i0+fftLen/4 */
        /* input is down scale by 4 to avoid overflow */
        /* T0 = yb, T1 = xb */
        T0 = pSrc16[i1 * 2u] >> 2u;
        T1 = pSrc16[(i1 * 2u) + 1u] >> 2u;

        /* writing the butterfly processed i0 + fftLen/4 sample */
        /* writing output(xc', yc') in little endian format */
        pSrc16[i1 * 2u] = out1;
        pSrc16[(i1 * 2u) + 1u] = out2;

        /*  Butterfly calculations */
        /* input is down scale by 4 to avoid overflow */
        /* U0 = yd, U1 = xd) */
        U0 = pSrc16[i3 * 2u] >> 2u;
        U1 = pSrc16[(i3 * 2u) + 1u] >> 2u;

        /* T0 = yb-yd, T1 = xb-xd) */
        T0 = __SSAT(T0 - U0, 16u);
        T1 = __SSAT(T1 - U1, 16u);
        /* R0 = (ya-yc) - (xb- xd) , R1 = (xa-xc) + (yb-yd) */
        R0 = (q15_t) __SSAT((q31_t) (S0 + T1), 16);
        R1 = (q15_t) __SSAT((q31_t) (S1 - T0), 16);
        /* S = (ya-yc) + (xb- xd), S1 = (xa-xc) - (yb-yd) */
        S0 = (q15_t) __SSAT((q31_t) (S0 - T1), 16);
        S1 = (q15_t) __SSAT((q31_t) (S1 + T0), 16);

        /* co1 & si1 are read from Coefficient pointer */
        Co1 = pCoef16[ic * 2u];
        Si1 = pCoef16[(ic * 2u) + 1u];
        /*  Butterfly process for the i0+fftLen/2 sample */
        /* xb' = (xa-yb-xc+yd)* co1 - (ya+xb-yc-xd)* (si1) */
        out1 = (q15_t) ((Co1 * S0 - Si1 * S1) >> 16u);
        /* yb' = (ya+xb-yc-xd)* co1 + (xa-yb-xc+yd)* (si1) */
        out2 = (q15_t) ((Si1 * S0 + Co1 * S1) >> 16u);
        /* writing output(xb', yb') in little endian format */
        pSrc16[i2 * 2u] = out1;
        pSrc16[(i2 * 2u) + 1u] = out2;

        /* Co3 & si3 are read from Coefficient pointer */
        Co3 = pCoef16[3u * ic * 2u];
        Si3 = pCoef16[(3u * ic * 2u) + 1u];
        /*  Butterfly process for the i0+3fftLen/4 sample */
        /* xd' = (xa+yb-xc-yd)* Co3 - (ya-xb-yc+xd)* (si3) */
        out1 = (q15_t) ((Co3 * R0 - Si3 * R1) >> 16u);
        /* yd' = (ya-xb-yc+xd)* Co3 + (xa+yb-xc-yd)* (si3) */
        out2 = (q15_t) ((Si3 * R0 + Co3 * R1) >> 16u);
        /* writing output(xd', yd') in little endian format */
        pSrc16[i3 * 2u] = out1;
        pSrc16[(i3 * 2u) + 1u] = out2;

        /*  Twiddle coefficients index modifier */
        ic = ic + twidCoefModifier;

        /*  Updating input index */
        i0 = i0 + 1u;

    }
    while(--j);

    /*  End of first stage process */

    /* data is in 4.11(q11) format */


    /*  Start of Middle stage process */

    /*  Twiddle coefficients index modifier */
    twidCoefModifier <<= 2u;

    /*  Calculation of Middle stage */
    for (k = fftLen / 4u; k > 4u; k >>= 2u)
    {
        /*  Initializations for the middle stage */
        n1 = n2;
        n2 >>= 2u;
        ic = 0u;

        for (j = 0u; j <= (n2 - 1u); j++)
        {
            /*  index calculation for the coefficients */
            Co1 = pCoef16[ic * 2u];
            Si1 = pCoef16[(ic * 2u) + 1u];
            Co2 = pCoef16[2u * ic * 2u];
            Si2 = pCoef16[2u * ic * 2u + 1u];
            Co3 = pCoef16[3u * ic * 2u];
            Si3 = pCoef16[(3u * ic * 2u) + 1u];

            /*  Twiddle coefficients index modifier */
            ic = ic + twidCoefModifier;

            /*  Butterfly implementation */
            for (i0 = j; i0 < fftLen; i0 += n1)
            {
                /*  index calculation for the input as, */
                /*  pSrc16[i0 + 0], pSrc16[i0 + fftLen/4], pSrc16[i0 + fftLen/2], pSrc16[i0 + 3fftLen/4] */
                i1 = i0 + n2;
                i2 = i1 + n2;
                i3 = i2 + n2;

                /*  Reading i0, i0+fftLen/2 inputs */
                /* Read ya (real), xa(imag) input */
                T0 = pSrc16[i0 * 2u];
                T1 = pSrc16[(i0 * 2u) + 1u];

                /* Read yc (real), xc(imag) input */
                S0 = pSrc16[i2 * 2u];
                S1 = pSrc16[(i2 * 2u) + 1u];


                /* R0 = (ya + yc), R1 = (xa + xc) */
                R0 = __SSAT(T0 + S0, 16u);
                R1 = __SSAT(T1 + S1, 16u);
                /* S0 = (ya - yc), S1 = (xa - xc) */
                S0 = __SSAT(T0 - S0, 16u);
                S1 = __SSAT(T1 - S1, 16u);

                /*  Reading i0+fftLen/4 , i0+3fftLen/4 inputs */
                /* Read yb (real), xb(imag) input */
                T0 = pSrc16[i1 * 2u];
                T1 = pSrc16[(i1 * 2u) + 1u];

                /* Read yd (real), xd(imag) input */
                U0 = pSrc16[i3 * 2u];
                U1 = pSrc16[(i3 * 2u) + 1u];

                /* T0 = (yb + yd), T1 = (xb + xd) */
                T0 = __SSAT(T0 + U0, 16u);
                T1 = __SSAT(T1 + U1, 16u);

                /*  writing the butterfly processed i0 sample */
                /* xa' = xa + xb + xc + xd */
                /* ya' = ya + yb + yc + yd */
                pSrc16[i0 * 2u] = ((R0 >> 1u) + (T0 >> 1u)) >> 1u;
                pSrc16[(i0 * 2u) + 1u] = ((R1 >> 1u) + (T1 >> 1u)) >> 1u;

                /* R0 = (ya + yc) - (yb + yd), R1 = (xa + xc) - (xb + xd) */
                R0 = (R0 >> 1u) - (T0 >> 1u);
                R1 = (R1 >> 1u) - (T1 >> 1u);

                /* (ya-yb+yc-yd)* (si2) - (xa-xb+xc-xd)* co2 */
                out1 = (q15_t) ((Co2 * R0 - Si2 * R1) >> 16);
                /* (ya-yb+yc-yd)* co2 + (xa-xb+xc-xd)* (si2) */
                out2 = (q15_t) ((Si2 * R0 + Co2 * R1) >> 16);

                /*  Reading i0+3fftLen/4 */
                /* Read yb (real), xb(imag) input */
                T0 = pSrc16[i1 * 2u];
                T1 = pSrc16[(i1 * 2u) + 1u];

                /*  writing the butterfly processed i0 + fftLen/4 sample */
                /* xc' = (xa-xb+xc-xd)* co2 - (ya-yb+yc-yd)* (si2) */
                /* yc' = (ya-yb+yc-yd)* co2 + (xa-xb+xc-xd)* (si2) */
                pSrc16[i1 * 2u] = out1;
                pSrc16[(i1 * 2u) + 1u] = out2;

                /*  Butterfly calculations */
                /* Read yd (real), xd(imag) input */
                U0 = pSrc16[i3 * 2u];
                U1 = pSrc16[(i3 * 2u) + 1u];

                /* T0 = yb-yd, T1 = xb-xd) */
                T0 = __SSAT(T0 - U0, 16u);
                T1 = __SSAT(T1 - U1, 16u);

                /* R0 = (ya-yc) - (xb- xd) , R1 = (xa-xc) + (yb-yd) */
                R0 = (S0 >> 1u) + (T1 >> 1u);
                R1 = (S1 >> 1u) - (T0 >> 1u);

                /* S1 = (ya-yc) + (xb- xd), S1 = (xa-xc) - (yb-yd) */
                S0 = (S0 >> 1u) - (T1 >> 1u);
                S1 = (S1 >> 1u) + (T0 >> 1u);

                /*  Butterfly process for the i0+fftLen/2 sample */
                out1 = (q15_t) ((Co1 * S0 - Si1 * S1) >> 16u);
                out2 = (q15_t) ((Si1 * S0 + Co1 * S1) >> 16u);
                /* xb' = (xa-yb-xc+yd)* co1 - (ya+xb-yc-xd)* (si1) */
                /* yb' = (ya+xb-yc-xd)* co1 + (xa-yb-xc+yd)* (si1) */
                pSrc16[i2 * 2u] = out1;
                pSrc16[(i2 * 2u) + 1u] = out2;

                /*  Butterfly process for the i0+3fftLen/4 sample */
                out1 = (q15_t) ((Co3 * R0 - Si3 * R1) >> 16u);

                out2 = (q15_t) ((Si3 * R0 + Co3 * R1) >> 16u);
                /* xd' = (xa+yb-xc-yd)* Co3 - (ya-xb-yc+xd)* (si3) */
                /* yd' = (ya-xb-yc+xd)* Co3 + (xa+yb-xc-yd)* (si3) */
                pSrc16[i3 * 2u] = out1;
                pSrc16[(i3 * 2u) + 1u] = out2;


            }
        }
        /*  Twiddle coefficients index modifier */
        twidCoefModifier <<= 2u;
    }
    /*  End of Middle stages process */


    /* data is in 10.6(q6) format for the 1024 point */
    /* data is in 8.8(q8) format for the 256 point   */
    /* data is in 6.10(q10) format for the 64 point  */
    /* data is in 4.12(q12) format for the 16 point  */

    /* start of last stage process */


    /*  Initializations for the last stage */
    n1 = n2;
    n2 >>= 2u;

    /*  Butterfly implementation */
    for (i0 = 0u; i0 <= (fftLen - n1); i0 += n1)
    {
        /*  index calculation for the input as, */
        /*  pSrc16[i0 + 0], pSrc16[i0 + fftLen/4], pSrc16[i0 + fftLen/2], pSrc16[i0 + 3fftLen/4] */
        i1 = i0 + n2;
        i2 = i1 + n2;
        i3 = i2 + n2;

        /*  Reading i0, i0+fftLen/2 inputs */
        /* Read ya (real), xa(imag) input */
        T0 = pSrc16[i0 * 2u];
        T1 = pSrc16[(i0 * 2u) + 1u];
        /* Read yc (real), xc(imag) input */
        S0 = pSrc16[i2 * 2u];
        S1 = pSrc16[(i2 * 2u) + 1u];

        /* R0 = (ya + yc), R1 = (xa + xc) */
        R0 = __SSAT(T0 + S0, 16u);
        R1 = __SSAT(T1 + S1, 16u);
        /* S0 = (ya - yc), S1 = (xa - xc) */
        S0 = __SSAT(T0 - S0, 16u);
        S1 = __SSAT(T1 - S1, 16u);

        /*  Reading i0+fftLen/4 , i0+3fftLen/4 inputs */
        /* Read yb (real), xb(imag) input */
        T0 = pSrc16[i1 * 2u];
        T1 = pSrc16[(i1 * 2u) + 1u];
        /* Read yd (real), xd(imag) input */
        U0 = pSrc16[i3 * 2u];
        U1 = pSrc16[(i3 * 2u) + 1u];

        /* T0 = (yb + yd), T1 = (xb + xd) */
        T0 = __SSAT(T0 + U0, 16u);
        T1 = __SSAT(T1 + U1, 16u);

        /*  writing the butterfly processed i0 sample */
        /* xa' = xa + xb + xc + xd */
        /* ya' = ya + yb + yc + yd */
        pSrc16[i0 * 2u] = (R0 >> 1u) + (T0 >> 1u);
        pSrc16[(i0 * 2u) + 1u] = (R1 >> 1u) + (T1 >> 1u);

        /* R0 = (ya + yc) - (yb + yd), R1 = (xa + xc) - (xb + xd) */
        R0 = (R0 >> 1u) - (T0 >> 1u);
        R1 = (R1 >> 1u) - (T1 >> 1u);

        /* Read yb (real), xb(imag) input */
        T0 = pSrc16[i1 * 2u];
        T1 = pSrc16[(i1 * 2u) + 1u];

        /*  writing the butterfly processed i0 + fftLen/4 sample */
        /* xc' = (xa-xb+xc-xd) */
        /* yc' = (ya-yb+yc-yd) */
        pSrc16[i1 * 2u] = R0;
        pSrc16[(i1 * 2u) + 1u] = R1;

        /* Read yd (real), xd(imag) input */
        U0 = pSrc16[i3 * 2u];
        U1 = pSrc16[(i3 * 2u) + 1u];
        /* T0 = (yb - yd), T1 = (xb - xd) */
        T0 = __SSAT(T0 - U0, 16u);
        T1 = __SSAT(T1 - U1, 16u);

        /*  writing the butterfly processed i0 + fftLen/2 sample */
        /* xb' = (xa-yb-xc+yd) */
        /* yb' = (ya+xb-yc-xd) */
        pSrc16[i2 * 2u] = (S0 >> 1u) - (T1 >> 1u);
        pSrc16[(i2 * 2u) + 1u] = (S1 >> 1u) + (T0 >> 1u);


        /*  writing the butterfly processed i0 + 3fftLen/4 sample */
        /* xd' = (xa+yb-xc-yd) */
        /* yd' = (ya-xb-yc+xd) */
        pSrc16[i3 * 2u] = (S0 >> 1u) + (T1 >> 1u);
        pSrc16[(i3 * 2u) + 1u] = (S1 >> 1u) - (T0 >> 1u);
    }
    /* end of last stage  process */

    /* output is in 11.5(q5) format for the 1024 point */
    /* output is in 9.7(q7) format for the 256 point   */
    /* output is in 7.9(q9) format for the 64 point  */
    /* output is in 5.11(q11) format for the 16 point  */

#endif /* #ifndef ARM_MATH_CM0_FAMILY */

}
